Hi,
In case you are not already aware, you need to have Active Azure Developer Associate (AZ-204) or Active Azure Administrator (AZ-104) certification in addition to passing AZ-400 to earn DevOps Engineer Expert certification.
If you do have at least one of the prerequisite certifications above your certification should be on your Certifications tab. If it isn't you need to ask a question in Microsoft Credentials forum and a support moderator will assist you. Below is link to ask question over there:
https://trainingsupport.microsoft.com/en-us/newthread?threadtype=Questions&forum=mcp
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP